Shin-Etsu Chemical Co Ltd disclosed that its Nd-Fe-B (neodymium-iron-boron)-based magnet was employed for the drive motor of Nissan Motor Co Ltd's Leaf electric vehicle (EV).
The magnet is "Nxx-G." It uses less dysprosium (Dy), which enhances the holding power of the motor, than other Nd-Fe-B-based magnets.
At Techno-Frontier 2011, which took place from July 20 to 22, 2011, in Japan, Shin-Etsu Chemical exhibited a cutaway model of the Leaf's motor equipped with the company's magnet. The Nd-Fe-B-based magnet has an angular shape. About 30% of the magnet consists of Nd, B and Dy, and the rest 70% consists of Fe. Dy seems to account for about 10% of the magnet.
To reduce the ratio of Dy, Shin-Etsu Chemical developed a manufacturing method called "grain boundary diffusion alloying method." It enables to reduce the amount of Dy by about 60% while maintaining the holding power.
In a traditional manufacturing method, Nd, Fe, B and Dy are mixed at the same time and sintered. In this method, Dy exists homogeneously in the magnet. However, Shin-Etsu Chemical found that the Dy on the surface of the magnet is important for improving holding power and the Dy inside the magnet does not contribute to it much.
Therefore, in the grain boundary diffusion alloying method, after making a magnet that does not contain Dy, the magnet is impregnated with Dy solution from the outside. As a result, Dy is added only near the surface of the magnet, and the amount of Dy can be reduced without decreasing the holding power.